Epitaxial deposition reactor



2 Sheets-Sheet 1 Filed July 29, 1965 TE NR wm l. mH M. F

.EE- m... R A R 2 3 3 m... M l L v 6 4 6 B ,3 3 0 44 7 2 3 3 4 l 2 3 4Il; I wl. |i1l|1f .l ,v w v l n X 4 |r a u \l\ )r IMM M 9 5 B E 7l k w m6 B /l ATTORNEY Jan. 27, 1970 D, M. HARRIS 3,491,720

EPITAXIAL DEPOSITION REACTOR Filed July 29, 1965 2 Sheets-Sheet 2 I ,722 le I9 2' I- 14 f ll- B u', lmmllmlnuurl I9 E/Zl E 5 ii. l* I6'B I*'glmmlumuul 2 22 HHIW. FIG. 3

INVENTOR DARREL M. HARRIS wwf/.MW

ATTORNEY United States Patent O 3,491,720 EPITAXIAL DEPGSITION REACTORDarrel M. Harris, Kirkwood, Mo., assignor to Monsanto Company, St.Louis, Mo., a corporation of Delaware Filed July 29, 1965, Ser. No.475,722 Int. Cl. C23c 13/08 U.S. Cl. 11S-49.5 6 Claims ABSTRACT OF THEDISCLOSURE An apparatus used in the epitaxial deposition of epitaxialcoatings on semiconductor wafers. The apparatus includes a housingsubdivided into three chambers. The lower chamber forms a react-ionchamber in which a heating element may be disposed and which in turnsupports a plurality of semiconductor wafers to receive an epitaxia-lcoating. Located above the lower chamber is an upper chamber whichconstitutes a purging chamber. A second heating element may be -disposedin this chamber and subjected to a purging atmosphere during thedeposition of an epitaxial coa-ting on the wafers in the lower chamber.A third chamber is provided proximate the second chamber for admissionand withdrawal of the heating elements from lthe second chamber. In thismanner, a somewhat continuous operation involving the deposition ofepitaxial coatings on wafers may be performed. Common wall means formingeach pair of adjacent chambers include removable closure means. Thehousing has glove means sealed to an opening therein whereby an operatormay manipulate said closures and heating elements.

This invention relates in general to certain new and useful improvementsin epitaxial deposition reactors, and more particularly, to an improvedapparatus for producing epitaxial deposition coatings on semiconductorbodies.

In recent years, semiconductor devices such as silicon controlledrectifier-s have found widespread use in the electronics industry.Semiconductor devices which comprise a plurality of layers ofsemiconductor ma-terial having different conductivities and separated bya transition zone have proved to be very elfective in many electronicdevices. These semiconductor devices having at least two layers ofdifferent conductivities with a transition region therebetween are verysuitable for use in the formation of electronic members such as diodes,transistors, switches and similar types of electronic structures.

One very elfective method of producing semiconductor devices is by theepitaxial deposition of silicon on a wafer formed of' like material.Generally, the wafer-s involved must be formed of a high purity silicon,however, doped to a specilied resistivity. These silicon wafers are thennormally placed on an electrical resistance heating element which issecured to the electrical contacts of an epitaxial silicon furnace, andare heated to a temperature where free silicon is deposited on the waferland becomes bonded to the surface of the wafer. One effective method ofproducing the free silicon which forms the epitaxial layer on thesilicon wafers is by the reduction of gaseous tnichlorosilane. Thesewafers are then further processed by conventional methods and used inthe manufacture of the above solid-state devices.

In recent years, it has become a common practice to employ resistanceheating elements formed of graphite in these epitaxial silicon furnaces.The heating elements are generally U-shaped in horizontal cross sectionand consist of a pair of legs which are connected by a bight portion.The legs are generally provided with terminal connectors at their freeend, that is the ends remote from the bight portion for ultimateconnection to the contacts of the 3,491,720 Patented Jan. 27, 1970deposition furnace. A suitable amount of electrical current is thenpassed lth-rough the heating element to heat Ithe element to the desiredreaction temperature. Generally, the heating element is enclosed withina bell jar, which is normally formed of a quartz or other high siliconcontent material and which is preferably transparent. The bell jar orso-called hat is suitably secured to a base plate forming part of thefurnace and also encloses the gas jets permitting entry of the gas intothe bell jar.

It has been a common practice in the prior art to position these heatingelements or so-called bridges in a substantially horizontal posi-tion sothat the silicon wafers may be deposited directly upon the upper surfaceof the heating element. However, a horizontally disposed bridge hasproved to be rather ineffective, particularly Where it is desired toproduce a large number of epitaxial silicon wafers in a singleoperation. It appeared as though the gas ow deposited the greaterportion of the silicon on the wafers near the free end of the heatingelement. The gas jets of the silicon bearing material and the reductionmaterial, which was generally hydrogen entered beneath the bridge sothat the gas would flow beneath the bridge around the free ends and overthe upper portion thereof. During the reaction between the gases, thefree silicon thus formed would then become deposited on the uppersurface of the silicon wafer. However, much of the silicon containedwithin the feed `gases was consumed and -the wafers near the contactends of the heating element received substantially lesser quantities ofsilicon layers. Moreover, it was diicult to maintain uniformity ofthickness in the epitaxial layers in this type of opera-tion.

Aside from the above problems, the heating elements were generally smallin their construction by reason of the fact that they were almost alwaysmounted in cantilever positions. Because of the fact that they wereconstructed of electrical resistance material, they were not inherentlystrong and consequently, the legs could not accommodate a large numberof silicon wafers. Therefore, the wafers had to be very carefully placedon the legs of the heating element so that a maximum amount of bridgearea was employed in each epitaxial deposition operation. Accordingly, agreat deal of labor time was consumed in this operation, whichmaterially increased the cost of each of the silicon wafers.

The bell jars employed in the prior art technique also created a numberof problems which materially increased the labor time consumed in eachoperation and therefore materially increased the cost of silicon wafersproduced. In the case where it is desired to produce deposition coatingson silicon wafers, a silicon bearing feed gas is admitted to thereaction chamber. One common technique to to feed trichlorosilane andhydrogen to the reaction chamber thereby reacting the gases at highternperature and forms an elemental silicon deposit on the surface ofthe silicon Iwafers in the chamber. However, the residue products andthe silicon bearing gases have a tendency to react to form long chainedsilicon bearing polymers where silicon forms part of the backbone of thepolymer chain. This polymer tends to collect on the interior surfaces ofthe bell jar and adhere to the interior wall of the bell jar. Thisproblem is primarily prevalent in stainless steel bell jars. Thiscollection of a polymer on the wall of the bell jar produces no realproblem during the expitaxial deposition operation. However, after thebell jar is substantially cooled and removed permitting access to theheating element, the interior surface of the jar is exposed to theatmosphere. The polymer by its very nature is very hydroscopic andhydrolyzes when exposed to moist air. The hydrolized polymer thenbecomes very tightly adherent to the interior wall of the bell jar andbecomes very difficult to remove. Not only does the presence of thepolymer produce an unsightly appearance, but it also has a tendency tobreak up into small particles which become deposited on the lwafersurface and subsequently interfere with particles in succeedingepitaxial deposition reaction. Accordingly, it is necessary to removethis collected silicon containing polymer from the interior surfaces ofthe bell jar after each deposition operation. This down-time is not onlycostly from the increased labor standpoint, but either prevents the useof the deposition furnace or the necessity -of an inventory of a numberof bell jars which can be employed.

Another problem often encountered with epitaxial deposition furnacespresently available is that much of the time employed in the operationfor depositing epitaxial layers is consumed in preparatory processes.Generally,rit is necessary to purge the atmosphere of the reactionchamber before admitting the feed gases in order to insure completeremoval of any foreign matter. Furthermore, it is often necessary toeven purge the heating element and the wafers contained thereon prior tothe actual deposition of an epitaxial layer on the wafers. This type ofprocess consumes a great deal of time in the epitaxial silicon furnaceand also consumes a great deal of manual labor Vwhich is required toperform these purging operations.

It is, therefore the primary object of the present invention to providean apparatus which is capable of producing epitaxial deposition layerson semiconductor material to produce a semiconductor body having atleast two layers with a transition region therebetween.

It is another object of the present invention to provide an apparatus ofthe type stated which is capable of producing epitaxial depositionlayers on a plurality of Wafers where each of the layers has asubstantially uniform thickness.

It is a further object of the present invention to provide an apparatusof the type stated which includes at least one chamber for purging theheating element prior to the deposition operation, and at least onechamber for producing the epitaxial deposition coatings.

It is also an object of the present invention to provide an apparatus ofthe type stated which required a minimum amount of manual laborattention.

It is another salient object of the present invention to provide anapparatus of the type stated which is highly eiiicient in its operationand is relatively inexpensive to manufacture.

With the above and other objects in view, my invention resides in thenovei features of form, construction, arrangement, and combination ofparts presently described and pointed out.

In the accompanying drawings (2 sheets):

FIGURE 1 is a vertical sectional view of an apparatus for producingsemiconductor bodies which is constructed in accordance with andembodies the present invention;

FIGURES 2 and 3 are horizontal sectional views taken along lines 2--2and 3 3, respectively, of FIGURE l;

FIGURE 4 is a fragmentar;J sectional view taken along line 4-4 of FIGURE2;

FIGURE 5 is a fragmentary sectional View taken along line 5-5 of FIGURE1; and

FIGURE 6 is a fragmentary sectional view taken along line 6-6 of FIGURE1.

GENERAL DESCRIPTION Generally speaking, the present invention relates toan apparatus for producing a plurality of uniform semiconductor bodieshaving a plurality of layers of semiconductor materials with differentconductivities and where each of the layers is separated by a transitionregion. The various layers are of a single crystal structure and havedifferent conductivities, either in type or in degree.

The present. invention provides an apparatus ywhich generally comprisesa housing subdivided into three chambers. The lower .chamber which iswater cooled forms the reaction chamber and includes a pair of electrodeclamps for holding a vertically disposed heating element. The heatingelement includes a number oi wafer positions with means for holding thewafers -while the heating element is disposed in the substantiallyvertical position. Moreover, the electrode clamps have externallyextending handles for securing the heating element within the electrodesby means external to the reaction cham ber. A pair of diametrallyopposed gas jets are disposed along the upper margin of the reactionchamber and admit the feed gases in downwardly directed streams.Disposed above the reaction chamber is a second charnber whichconstitutes a purging chamber. A removable cover plate providesoperative communication between the reaction chamber and the purgingchamber. The purging chamber is also provided with gas inlets and gasoutlets for admission and -witbdrawal of purging gases. Moreover, thesecond chamber is provided with a means for retaining another heatingelement which is ultimately to be disposed in the reaction chamber.Finally, a third chamber is provided with a removable closure plateproviding operative communication to the second chamber. The thirdchamber is similarly provided with gas inlet and outlet ports foradmission and 'withdrawal of purging gases. The third chamber is alsoprovided with a removable lclosure plate for access to the third chamberand operative communication to the external atmosphere.

Thus, heating elements are operativelg.l disposed in the first andsecond chambers and purging gas is admitted t0 each of these chambers.The atmosphere in each of the chambers is purged and the heatingelements are cleansed during the time that feed gases are admitted tothe re= action chamber for depositing epitaxial deposition layers onwafers which are, in turn, a supported on a heating element in thereaction chamber. After a suiiicient epitaxial layer has been depositedon the wafers in the reaction chamber, the heating elements are allowedt0 cool and the electrode clamps are released permitting removal of theheating element in the reaction chamber. Suitable hand gloves areprovided for shifting the position of the heating elements in thevarious reaction chambers. The heating element in the reaction chamberis then shifted to the purging chamber and the heating element in thepurging chamber is then shifted to the reaction chamber. Moreover, theheating element in the third chamber and the heating element which hasjust received the epitaxial coating are then changed in position wherethe heating element is ultimately removed to the atmosphere and theheating element which initially was disposed in the third chamber isthen prepared for entry into the reaction chamber.

The heating elements which are provided fer use in the present inventionare designed so that each of the legs thereof is provided withsuflicient area to accommodate at least one or two rows of waiers oneach of the legs. Each of the rows is provided with a plurality of waferpositions where each wafer is secured to the heating element. By the useof pins which extend through the heating element or so-called bridge, aplurality of wafers may be mounted on each flat surface of the legs,thereby substantially increasing the capacity of the heating elements.

The foregoing process may be employed in the formation of semiconductorbodies of known semiconductor material, the only criterion being that adecomposable vapor source of the material is available. The termsthermally decomposable, termal decomposition, and the associated depositof a product of decomposition as used herein are intended to be genericto the mechanism of the decomposition and reduction of various siliconcontaining gases such as trichlorosilane and the liberation of siliconatoms through the action of reducing gases and heat on such siliconbearing gases or mixtures thereof. These terms are also generic to andare included within the concept of the mechanism of high temperaturereactions where high temperature causes interaction between variousmaterials with the liberation of specific materials or atoms.

DETAILED DESCRIPTION Referring now in more detail and by referencecharacters to the drawings which illustrate a preferred embodiment ofthe present invention, A designates an app-aratus for producingsemiconductor bodies of substantial area and planarity having aplurality of layers of different conductivities with transition regionstherebetween.

The apparatus A generally comprises a base plate 1 upon which is mounteda segmented housing 2, substantially as shown in FIGURE l. The housing 2is provided with a reaction chamber 3 formed by an annular side wall 4,the latter being formed of stainless steel or similar metals which canbe employed in the construction of the housing 2. Stainless steel ispreferred because of its internal strength and because of the fact thatit does not interfere with the reaction gases. Generally, stainlesssteel, such as Type 304 stainless steel is inert to feed gases such astrichlorosilane under the reaction conditions employed herein and,therefore, does not emit any impurities which may interfere with thereacting gases. The housing 2 is provided with a base flange 5 which isseated in facewise engagement with the upper surface of the base plate 1and provides an air-tight seal through a sealing ring 6. The annularside wall 4 is similarly provided with an annular top ange 7 whichsupports a top plate 8, the latter being held in fluid-tight engagementby means of a sealing ring 9 interposed between the ange 7 and the plate8. By reference to FIGURE l, it can be seen that the housing 2 issegmented vso that it is adaptable to rapid assembly and disassembly forinterchange of parts such as gas jets and sight glasses. The side wall 4is provided with a pair of conventional sight glasses or so-called sighttubes 10, 11, the sight tube 11 being angularly disposed in the manneras illustrated in FIG- URE 1. By further reference to FIGURE l, it canbe seen that the various components forming the reaction chamber 3 aredouble-walled or jacketed forming a cooling chamber for recirculating acooling water. It can be seen that the major portion of the stainlesssteel surface exposed to the interior of the chamber 3 is jacketed.Furthermore, these various jacketed sections are provided with theconventional fluid inlet and outlet fittings for connection to asuitable source of coolant (not shown).

Operatively mounted in the upper end of the side Wall 4 are a pair ofdiametrally opposed gas jets 12 which are in turn connected to suitablesources of feed gases (not shown) by means of flexible tubes 13. The gasjets 12 are conventional in their construction and are, therefore, notdescribed in detail herein. However, it should be understood that anysuitable gas jet which is normally employed in epitaxial depositionfurnaces is suitable for employment in the apparatus A. Similarly formedin the base plate 1 is a discharge port 14 for removal of the spent orexhaust gases from the reaction chamber 3. It can be seen that thedischarge port 14 is provided with a coupling 15 for removal of thespent gases and in turn communicates with the chamber 3. A suitablemanually operable valve may be connected to the coupling 15 forregulating the amount of spent gases discharged from the chamber 3.

Rigidly mounted on the upper surface of the base plate 1 and extendingupwardly into the chamber 3 are a pair of chucks or so-called clamps 16which serve as electrodes and to retain a suitable heating element 17,the latter to be hereinafter described in more detail. The chucks 16 areprovided with aligned slots 18 for accommodating the lower ends of theheating element 17, in the manner as shown in FIGURE 1 and moreover, can

be tightened and released by means of actuating rods 19, which extendoutwardly of the chamber 3 through an annular sealing ring 20. Theactuating rod 19 can be suitably provided with a handle 21 for releasingthe heating element 17 from the chuck 16. In this connection, it shouldbe understood that any suitable mechanical type of grasping means can beused to retain and release the heating element within the slot 18 bymeans of the actuating rod 19. The chucks 16, which serve as electrodes,are conventionally provided with terminals (not shown) by which they areconnected to a suitable source of electrical current (not shown) so thatas current flows through the contacts and the chucks 16, it will owthrough the heating elements 17 in order to raise the temperaturethereof. It should be pointed out that it is often desirable toinitially increase the temperatures of heating elements formed ofsilicon with a source of radiant energy since silicon has a highnegative resistance temperature coeiicient, or in other words, a highresistance to the passage of electrical current, when cooled.

The heating element 17 is of the type described in my copendingapplication No. 415,363, iiled Dec. 2, 1964, now U.S. Patent No.3,351,742 and has a pair of vertically disposed legs 22, which .areconnected by a horizontally disposed bight portion 23. The bridge 17 isof the double taper type where the legs are tapered from each of itstransverse ends in such manner that they have a slightly smallercross-sectional thickness at each of the ends than in the center portionthereof, when referring to the transverse dimension of the legs 22.Thus, it can be seen that the thicknesses of each of the legs increaseas the distance from the free ends thereof increases. The angle of taperof each of the legs is so adjusted that a cross-sectional area of eachof the legs 22 is maintained in order to provide a substantiallyconstant uniform temperature distribution across each of the legs. Thebight portion 23 is slightly thicker in the transverse dimension,reference being made to FIGURE 1 than the overall thickness of the legs22. For heaters having legs with an overall length of approximately 24inches, the legs have an overall thickness of approximately 0.260 at thecenter portion and a thickness of approximately 0.215 at each of theends. The bight portion 23 generally has an overall thickness ofapproximately 0.500 .and a relative height of approximately 15/3". Theheating element 17 is provided with a circular recess (not shown) at thepoint of connection of each of the two legs 22 with the bight portion 23and serves to create a substantially uniform temperature distributionacross the width of the bight portion 23. In essence, the recess forms aheat sink for heat dissipation in the region of high current density. Inthis manner, it can be seen that relatively even resistancecharacteristics are maintained throughout each of the legs 22 and thevbight portion 23 and, therefore, it is possible to maintain asubstantially uniform temperature distribution across the lengths ofeach of the legs.

It is also possible to maintain uniform temperature characteristicsthroughout the lengths of each of the heater legs 22 by selectivelyaltering the cross-sectional area in the manner also shown in mycopending application Ser. No. 415,363, filed Dec. 2, 1964, now U.S.Patent No. 3,351,742, dated Nov. 7, 1967. In this method, it isnecessary to measure the temperature produced at various selectedportions along the length and width of the heater legs. This can beconveniently accomplished by attaching thermalcouples to the heater andconnecting the leads thereof to a suitable temperature readout device.An optical pyrometer may also be employed. After the temperature :alongthe selected portions of the length of the heater legs has beenrecorded, the desired cross-sectional area can be obtained by removingthe required amount of this cross-sectional area. This is convenientlyaccomplished by vdrilling small apertures which are sufliciently smallso that they do not interfere with the internal strength of the heater,but yet are suicient in number so that they suiciently alter thecross-sectional area of the legs to provide proper resistancecharacteristics.

The material of construction of the bridges B is not necessarily limitedto graphite, inasmuch as the bridges B can be prepared from anyelectrically conductive material of high resistance which exhibits acharacteristic of becoming heated due to the passage of electricalcurrent therethrough. The bridges may be of material such as silicon, orconducting ceramics such as silicon carbide, or graphite or refractorymetals such as tantalum, molybdenum, or titanium. One importantcriterion is that the bridge must -be made of a material which does notcontain impurity atoms, or at least does not interact with the system byintroduction of impurity atoms.

The bridge may also be surface treated in the manner described in mycopending application Ser. No. 423,066, filed Jan. 4, 1965, now U.S.Patent No. 3,406,044, dated Oct. l5, 1968. In this procedure, freesilicon, which is produced by the reduction of gaseous trichlorosilane,is fused to the surface of the graphite heating element and reacts withthe carbon atoms of the heating element to form a tightly adherent,substantially permanent, gas impervious film. The graphite heatingelement is heated to a temperature where a portion of the silicon reactswith the carbon of the heating element to form a silicon carbide iilmand the remainder of the silicon, which becomes liquied, penetrates intothe pores of the graphite and becomes fused to the graphite. It has alsobeen found possible to deposit a silicon carbide coating on the surfaceof the bridge which is prepared by the simultaneous reduction oftrichlorosilane and chloroform. Here again, the silicon carbide becomesbonded to the surface of the graphite heating element. As a preferredembodiment, it has been found to be very acceptable to producealternating layers of silicon and silicon carbide and deposit theselayers on the surface of the heating element, all in the manner as morefully described in said copending application Ser. No. 423,066, iiledJan. 4, 1965, now U.S. Patent No. 3,406,044.

Wafers w of semiconductor material are prepared in .any suitable manner,as for example, slicing or cutting wafers from commercially availablezone reiined single crystals of semiconductor material. Both of thesemethods are well known in the prior art. It is important that the wafersare cut in such a manner that the surf-ace of the wafer to be treated isoriented in a specific crystallographic plane. Generally for thepurposes of the present invention, it is preferred that the wafers arecut or sliced in such a manner so that they are oriented in a (1-1-1)plane on the Miller indices. Naturally, the surface of the Wafer, whichis to receive the epitaxial deposition lm is carefully prepared by thegenerally accepted techniques of grinding, polishing, etching, andcleaning before the epitaXial deposition operation.

Each of the legs 22 is provided with two rows, each having a pluralityof longitudinally spaced wafer positions 24 and which are located sothat a Wafer w in one wafer position 24 is spaced a slight distance fromanother wafer w located in the next adjacent wafer position 24 in thesame row. In this manner, the maximum amount of the surface area of eachleg of the bridge 17 is employed. Each side of the legs 22 is providedwith marginally registered Wafer positions. By reference to FIG- URE 5,it can be seen that the inner wafer positions 24 have an inner wafer pin25 mounted slightly beneath the horizontal diameter of the waferposition and the outer Wafer positions `have pins 26 located slightlybelow the horizontal diameter of the Wafer position. The pins 25, 26 arelocated along the periphery of the Wafer positions 24 at an angle ofabout 20 to 30 below the horizontal centerline of the wafer position.The outer and inner wafer positions 24 share a common wafer supportingpin 27, which is located at the horizontal diameter of each of the waferpositions, substantially as shown in FIG- URE 5. The pin 27 is solocated that the upper peripheral margin thereof is tangential to thehorizontal centerline passing through the wafer position. Each of thepins 25, 26 is provided with extended ends 28 on each flat surface ofthe legs 22 and are provided with notches 29 on the transverse sides ofthe extended ends for engaging the peripheral margins of wafers wretained therein. The construction of the pins 25, 26 is more fullydescribed in my copending application Ser. No. 475,106, iiled July 27,1965, now U.S. Patent No. 3,391,270, dated July 2, 1968. Similarly, thecenter pin 27 is provided with notches on each transverse end forengaging both of the wafers w in each of the horizontally aligned Waferpositions 24. The pin 27 is similarly described in the aforementionedcopending application.

It is desirable to locate each of the pins 25, 26 and 27 as close to thehorizontal diameter of each of the wafer positions as possible. However,the pins 25, 26 must be located within the range of about 20 to 30 belowthe horizontal diameter in order to provide proper support. However, thecenter pin 27, which is common to both wafer positions 24 can be placedapproximately at the horizontal diameter of the wafer position inasmuchas each wafer positon has one outer pin 25, 26 located slightly belowthe horizontal diameter thereof. It is desirable to locate each of therespective'pins at the horizontal diameter in order to eliminate anypossibility of interference with gas ow. However inasmuch as theextended ends of the pins are relatively short with regard to theoverall thickness of the wafer w, the interference with the gas iiow isvery small. Moreover, these portions of the wafers immediately adjacentto the pins are generally removed in further processing operations wherethe wafer is employed to construct a semiconductor device.

It should be appreciated that by following the teachings of thisinvention, it is possible to form semiconductor bodies having aplurality of layers of differing conductivities. Moreover, the width ofeach of the layers may be precisely controlled by generally acceptedtechniques. This allows the transition region or junction to beaccurately positioned in the semiconductor body. Moreover, it is alsopossible to provide, in any layer formed, any variation in conductivitydesired in a plane which is parallel to the transition region by varyingthe concentration of vapor source of the active impurity atoms in theow.

An annular side Wall 30 having a substantially cylindrical horizontalcross section is disposed around the upper surface of the plate 8 andforms a purging chamber 31. The side wall 30 is provided with anoutwardly flaring annular base iiange 32 which is designed to engage theupper surface of the plate 8 and is sealed with respect thereto by meansof an annular sealing ring 33. The side wall 30 is also formed of thesame material used in the construction of the side wall 4 and preferablyis stainless steel. The annular side wall 30 is integrally formed withan outwardly aring annular top ange 34 and disposed thereon is arelatively thick circular viewing panel 35, which is sealed to theflange 34 by means of anannular sealing ring 36. The panel 35 may beformed of any suitable transparent material such as glass, quartz, orany synthetic material such as a polymethylmethacrylate orpolymethylacrylate. Moreover, on its upper surface the panel 35 has anannular recess for accommodating an annular metal retaining ring 37,which is provided with a plurality of annularly spaced outwardlyextending lobes 38. The lobes 38 are designed to match outwardlyextending lobes 39 on the base plate 1 and each is centrally aperturedto accommodate bolts 40, which are provided at their upper end With nuts41. In this manner, the two sections of the housing which consist of theside walls 4 and 30 may be removably secured in a gas-tight unitarystructure through the bolts 40. Moreover, the housing is easilydisassembled by removing the nuts 41 from the bolts and removing thevarious side walls 30.

The side wall 30 is similarly provided with a conventional sight glass42 which is similar to the previously described sight glass 10, and isdesigned to permit viewing of the chamber 31. Moreover, the side wall 30is suitably apertured and provided with the necessary supporting rings43, 44 to accommodate a gas inlet jet 45 and a discharge tube 46,respectively. The inlet jet 45 is connected to some suitable source ofpurging gas such as nitrogen or hydrogen (not shown) for purging theatmosphere of the chamber 31. The discharge tube 46 is suitablyconnected to some means for removing the spent gases from the chamber31. For optimum design, it is preferable to have the inlet jet 45located near the upper end of the side wall 30 and the discharge tube 46located near the lower end thereof, substantially as shown in FIGURE 1.The interior surface of the side wall 30 is provided with one or morehooks 47 for retaining heating elements similar to the heating element17. Moreover, the side wall 30 is suitably apertured to accommodate aconventional hand glove 48. The hand glove my be formed of a neoprenerubber or similar inert material which will not interfere with thepurging gases admitted to the chamber 31. Moreover, the hand glove 48must be formed of a materialy which will not contribute to anyimpurities in the atmosphere of the chamber 31 or which will create anyimpure condition on the surface of the heating element 17. The handglove 48 may be suitably mounted in the side wall 30 in any conventionalmanner, such as by means of an annular retaining ring provided withproper seals. The method of securing the hand glove 48 to the side wall30 is conventional in its construction, and is, therefore, neitherillustrated nor described in detail herein. It should be pointed out inthis connection, however, that the hand glove must be formed of a fairlythick rubber material which is capable of withstanding reduced pressureswithout expanding inasmuch as the chamber 31 can be subjected to reducedpressures if desired. Furthermore, the annular retaining ring may beannularly provided with a ange for accommodating a removable cover plate(not shown) if desired, when the chamber 31 is evacuated.

Communication is provided between the reaction chamber 3 and the purgingchamber 31 through an aperture 49 formed within the plate 8 and aremovable cover plate 50 is disposed thereover in the manner as shown inFIGURES 1 and 2. The cover plate 50 is secured to a conventional hinge51 which is, in tum, secured to the top plate 8. The cover plate 50 andthe top plate 8 are both jacketed and the top plate 8 is provided withfittings for connection to the source of coolant (not shown). Thecoolant chamber in the top plate 8 is connected to the coolant chamberof the cover plate 50 through flexible bellows substantially asillustrated in FIGURES v1 and 2.

The cover plate 50 is provided on its underface with an annular sealingring S2, which engages the upper surface of the plate 8 so that when thecover plate 50 is in its closed position, that is the position as shownin FIG- URE 1', a gas-tight seal will be maintained between the reactionchamber 3 and the purging chamber 31. The sealing ring 52 can be formedof a neoprene rubber or similar inert material which is capable ofcreating an airtight seal between the two chambers and is also capableof withstanding corrosion or deleterious effects from any of the gasesin the two chambers. It should also be understood that the sealing ring52 could be a sealing contact strip which is disposed on theundersurface of the plate 50 or alternatively on the upper surface ofthe top plate 8 so that a gas-tight seal is maintained between the coverplate 50 and the top plate 8 when the former is moved to its closedpositon. The cover plate 50 is retained in a closed position by means ofa pair of spring clamps 53, which are more fully illustrated in FIGURE4. The

spring clamps 53 are pivoted on pivot pins S4, which are, in turn,retained on the upper surface of the plate 8 by means of retainingbrackets 55. The spring clamps 53 consist of resilient arms 56, whichengage the upper surface of the cover plate 50, in the manner as shownin FIGURES 2 and 4.

The annular side wall 30 is cut away to accommodate a holding chambercabinet 57, the interior of which forms a holding chamber 58. Theholding cabinet 57 comprises top and bottom plates 59, 60, which arewelded or otherwise rigidly secured to the cut-away margins of the sidewall 30, in the manner as shown in FIGURE l. The annulus of the cutawayportion of the wall 30 may similarly be formed with gusset type platesor flanges for reinforcement of the top and bottom plates 59, 60. Weldedor otherwise rigidly secured to the plates 59, 60 are side walls 61,which form part of the cabinet 57. The side walls 61 are provided ateach of its transverse ends with outwardly extending door engagingflanges 62, 62'. Welded or otherwise rigidly secured to one of the sidewalls 61 are a pair of vertically spaced brackets 63 for hingedlyretaining a door I64. By reference to FIG'URE 2, it can -be seen thatthe door is pivotal with respect to the anges 62, 62', and is sealedthereagainst by means of an annular sealing ring 65, which may bemounted on the interior surface of the door 64 or upon the exteriorsurface of the flanges 62, 62 as desired. The door 64 is held in itsclosurewise position by means of a pair of upper and lower spring clamps66, which are substantially identical to the previously described springclamps 53, and consist of a resilient arm 67, secured to pivot pins 68,rwhich are in turn mounted on the upper and lower surfaces of the topand bottom plates 59, l60, respectively. The door 64, which providedaccess to the interior of the holding chamber 58 is provided with one ormore inwardly extending hooks 69 for retaining heating ele-ments similarto the heating element 17.

The interior surface of the annular side wall 30 is provided with a pairof vertically spaced brackets 70 in the area of the flanges 62, 62 foraccommodating an interior door 71, which is designed to closecommunication between purging chamber 31 and the holding chamber 58. Thedoor 71 is similarly mounted on conventional hinges 72, which are, inturn, secured to the brackets 70 andfmay be opened or closed as desired.The door 71 is similarly provided with a somewhat rectangular sealingring 73 along its peripheral margins and which abuts against theinterior anges 62, 62 when the door 71 is shifted to its closedposition, that is the position as shown in FIGURE 2. It should beunderstood in this connection that the sealing ring 73 could be mountedon the anges y62, 62 and designed to abut against the door 71, when thelatter is shifted to its closed position. A pair of upper and lowerclamps 74 are also provided for holding the door 71 in its closedposition. The clamps 74 are similar to the previously described clamps66 and cornprise fairly resilient arcuate ar-ms 75 which are pivotallymounted on the top and bottom plates 59, 60 by means of pivot pins 76.

By further reference to FIGURE l, it can be seen that the holdingchamber 58 can also be employed as a purging chamber and is, therefore,provided with a gas inlet jet 77, which is connected to a suitablesource of purging gas (not shown). The chamber 58 is also provided witha discharge port 78, which is, in turn, suitably connected to a meansfor accumulating the exhaust gases.

While the apparatus A generally illustrates a low pressure operatingdevice, it should be understood that the same could be modified withvery simple modifications so that the same is adaptable for highpressure operations. For example, the hand glove 48 could be constructedof a fairly heavy rubber material, which will not yield during highpressure operations, or the same could be replaced by a suitable rodactuating mechanism (not shown). A cover plate (not shown) could alsorbeemployed to cover the aperture leading to: the hand glove 48 asdescribed above. Moreover, the various clamps, suchas the clamps 66, 74could be replaced by a suitablefwing nut system where the various doorsare retained in a closurewise position, and more-over in a pres;sure-holding'position. Y

. OPERATION In use, the apparatus A may be easily assembled anddisassembled by means of the bolts 40 and the nuts 41. By removing thenuts 41 from the bolts 40, the various sections of the apparatus can bedisassembled and replaced when necessary. This segmented type ofconstruction provides increased utility.

In actual operation, a heating element or so-called bridge would bedisposed in each of the chambers 3, 31 and n58. For the purposes ofillustrating the present invention, it may be assumed that a bridgei17is disposed within each ofthe chambers and that a bridge loaded withsilicon wafers hastbeen secured to the electrode clamp1'6 in thereaction chamber 3. Furthermore, a bridge 17 is disposed bn the hook 47in the Ypurging chamber 31 and a bridge 17 isrdisposedion the hook 69 inthe reaction chamber 58. t the start of the cycle, the cover plate 50which is disposed in closurewise position over the aperture 49 is'openedthereby providing communication between the reaction chamber 3 and the.lpurging chamber 31. The heating element 17 is lowered by means of thehand glove 48 into the slot 18 and secured therein by means of theactuating rod 19 through the handle 21. The operation can observedthrough the sight glasses lii or llfThereafter, the cover plate Si) isclosed and locked by means of the clamps 53.

Y, Thereafter, feed gases are admitted to the reaction chamber V3 bymeans of the gas jets 12. Dry nitrogen at the rate of approximtely 50liters per minute is admitted to the reaction chamber 3 forapproximately 5 minutes Vin order to purge the atmosphere thereof.Thereafter, hydrogen is admitted to thereaction chamber 3 at the rate ofapproximately 75 liters per minute for approximately 5 minutes in orderto rid the chamber of any nitrogen content. Naturally, the nitrogen andhydrogen gases must be pure in orderrto prevent any contamination ofwafers disposed on the' heating element 17. It has been found inconnection with the present invention Ythat the original purgingoperation in the chamber 3 can be eliminated with no seriouscontamination effects, due to the fact that the chamber 3 is only Yincommunication with the chamber 31;'Currentris thereafter applied to theheating element 17 through the clamps 16 so" that the heating element israised to a temperature of at least 117 0 C. After the heating elementhas reached its equilibrium temperature conditions, the feed and dopantgases are then admitted to the chamber through Ythe jets Y12. The jets12 are suitably connected to a multiple position valve which permitsentry of the desired gas, such as the hydrogen, nitrogen or any of thefeed gases which are to be admitted. This type of construction isconventional and is, therefore, neither illustrated nor described indetail herein. yIt is to be noted that the gases wlich enter through thejets 12will follow somewhat of a circular path within the reactionchamber whereby the gases will ow downwardly and in close proximity tothe surfaces of the heating element 17 on which the wafers are disposedand upward alongVV the interior surfaces of the side wall 4. In thismanner, Ythe gases provide somewhat of a circular movement onV each sideof the'heating element 17. Some of the gasesof course, are Withdrawnthrough the discharge port 14 in order to maintain somewhat of anequilibrium pressure or desired pressure within the reaction chamber 3.A valve, of course, can be provided on the discharge port 14 forregulating the amount of exhaust gas which to be withdrawn from thereaction chamber 3. It has been foundY that by locating the gas jetsalong the upper surface of the reaction chamber 3, much improved'resultsare obtained. It was found that Ywhen the gas jets were located near thebase of the reaction chamber 3, complete gas cycles of the type hereindescribed were not obtained. Moreover, it has been found that byemploying two gasV jets a much more uniform and satisfactory surfacecoating is produced on each of the wafers supported on the heatingelement 17.

For further purposes of illustrating the present invention, it may beassumed that the wafers disposed on the heating element 17 are formed ofY,silicon afnd that the Ycoating to be epitaxially deposited on thewafter if.) is again anrepitaxial silicon coating. In this case, oneofthe feed gases would be a VVsilicon-.bearing gas. Generally preferredis trichlorosilane for use in producing an epitaxial silicon coating.The gaseous'ftrichlorosilane is' admitted to the reaction chamher 3 at arate of approximately 4 grams per minute for a period of about .20minutes to obtain a generally Ydesired film thickness. The time forfeeding the silicon bearing gas is determined by the thickness of theYepitaxial coating desired. Trichlorosilane reacts Ywith the hydrogen toform hydrogen chloride and free silicon, the latter of which isdeposited on'the surface of the wafers. Simultaneously with theadmission of the feed gas, 'Vadopant can also be added in order toobtain the desired epitaxial coating characteristics. For example, if itis desired tobtain an N-epitaxial layer, then phosphine or arsine may beadded to the feed gas, If, however, it is desired to obtain a P- type ofepitaxial coating, then a dopant such as diborane may be added to thefeed gas.

After the desired thickness of coating has been deposited on the wafersupported onV the heating element 17, the trichlorosilane feed gas anddopant gas is disontinued. However, the hydrogen feed 'gas is maintainedbut the temperature of the bridge is maintained at Vthe 117a temperaturein order to prevent contamination from the remaining quantities of feedgas in the reaction chamber 3. The hydrogen will react with theremaining quantities of feed gas thereby removing all free 'silicon orgases which are capable of producing free silicon from the atmosphereiThereafter, electrical current to the heating element 17 is discontinuedpermitting the bridge to cool. However, hydrogen feed is stillmaintained in order to aid in the cooling of the heating element 17. Thehydrogen purging is continued for approximately 10 minutesV after thepower to the heating element 17 is discontinued. Thereafter in order topurge the atmosphere in the chamber 3, nitrogen is admitted forapproximately 5 minutes. Y

While the epitaxial deposition process is carried on in the reactionchamber 3, the purging chamber 31 is continually purged with nitrogen.Accodringly, when the heating element 17 is removed from the chamber 3,the atmosphere in the purging chamber 31 will not provide anycontaminating atmosphere in the reaction chamber 3. f When it is desiredto change the two heating elements 17 in the reaction chamber 3 and-thepurging chamber 31, the Yactuating-rod 19 is turned, in order to releasethe heating element 17 and the clamps 116. The clamps 53 are openedpermitting the cover plate 50 to be swung to its open position.Thereafter, a hand inserted in the hand glove 48 can be extended intothe reaction chamber 3 for grasping the heating element 17 by the bightportion Z3 and pulling the same upwardly Vinto the purging chamber 31.The heating element 17 cari be hung on any suitable hook 47 Within thepurging chamber 31. Then, the heating element 17 which was disposed inthe purging chamber 31 can be moved into the reaction chamber 3 andshifted into' the slot 18 where it is retained by turning the rod 19 tolock the heating elementl 17 in the clamp 16. Thereafter, the door 50can be closed andV held in the closed position by means of the clamps53.V At this point, the door 71 can be opened permitting communicationbetween the chamber 31 and the holding chamber 58. A heating elementwhich was originally disposed in the chamber 58 is then shifted into thepurging chamber 3'1. The heating element which has just received theepitaxial coating can then be shifted into the holding chamber 58.Thereafter, the door 71 is closed and retained in the closed position bymeans of the clamps 74. While in the purging chamber, both the heatingelement and the chamber will be continually purged by nitrogen gas whichis continually admitted to the chamber 31. In order to remove theheating element which was removed from the reaction chamber 3, the door64 is opened by releasing the clamps `66. Thereafter, this latter namedheating element can be removed and the wafers removed from the heatingelement. A new heating element 17 is then disposed on the hook 69 andthe door `64 shifted to the closed position. It can be seen that as thisoccurs, the holding chamber 58 will be exposed to the atmosphere andthereby pick up contaminates fromv the atmosphere. However, thecontinual purging of the holding chamber 58 with nitrogen rapidlycleanses the atmosphere therein so that when the door 71 is opened, thechamber 31 does not receive any contaminates. Moreover, as an extraprecaution, the chamber 31 prevents any contamiates from entering thereaction chamber 3. Consequently, it can be seen that the reactionchamber 3 is almost permanently sealed from atmospheric conditions.

Moreover, it can also be seen that by purging the holding chamber 31 andthe holding chamber 58, not only is the atmosphere cleansed so thatcontaminates will enter through the chamber 3, but the heating elementsthemselves are also cleansed. In this manner, the original purging timenormally required in epitaxial deposition furnaces has beensubstantially reduced and consequently, more efficient operating timecan be obtained in the reaction chamber 3. Furthermore, as pointed outabove, the purging operation in the reaction chamber 3 can be eliminatedif desired without any serious consequence of contamination. It can alsobe seen that this cycle is con tinually maintained. After the wafers onthe heating element 17 in the reaction chamber 3 have received asufficient epitaxial deposition coating, the heating element 17 is thenremoved into the purging chamber 31 in the manner previously described.Similarly, the heating element in the purging chamber 31 is then shiftedinto the reaction chamber 3. The same shift thereafter takes placebetween the holding chamber 58 and the purging chamber 31.

It should be appreciated that by following the teachings of thisinvention, it is possible to form semiconductor bodies having aplurality of layers of differing conductivities. Moreover, the width ofeach of the ylayers may be precisely controlled by generally acceptedtechniques. This allows the transition region or junction to beaccurately positioned in the semiconductor body. Moreover, it is alsopossible to provide in any layer formed, any variation in conductivitydesired in a plane which is parallel to the transition region by varyingthe concentration of vapor source of the active impurity atoms in theflow.

It can also be seen that any desired type of semiconductor device may bemade by utilizing the methods and the apparatus of the presentinventiomln each case, the semiconductor device will have at least twolayers of semiconductor material with different conductivities and eachof the layers being separated by a transition region. vIn someinstances, the transition region will bea P-N junction, where in othercases', it may be a P-I or an N-I junction. In some cases as desired,there may be a sharp transition region between layers of high and lowresistivity material of the same conductivity type. It should also beappreciated that the invention may be employed in the formation ofsemiconductor bodies having a plurality of layers of semiconductormaterial of differing conductivities separated by a transition region.It should be understood that each of the layers may be the samesemiconductor material and other than silicon, for example, siliconcarbide, various group 3-5 compounds, such as gallium arsenide, indiumantimonide, gallium phosphide, and similar types of material. Naturally,the individual layers of these latter groups of compounds may be formedof different semiconductor materials. IIt is, however, that essentiallysingle crystal growth is maintained and hence, strong consideration mustbe given when depositing layers of dissimilar material to thecrystallography of the layer on which the growth occurs in order topreserve the single crystal characteristics to the greatest degreepossible.

It should be understood that changes and modifications in the form,construction, arrangement and combination parts presently described andpointed out may be made and substituted for those herein shown withoutdeparting from the nature and principle of my invention.

Having thus described my invention what I desire to claim and secure byLetters Patent is:

1. An apparatus for depositing an epitaxial coating 0n a semiconductormaterial removably disposed on a material holder, said apparatuscomprising base means, a housing operatively attached to said basemeans, means in said housing forming first and second chambers, a commonwall extending between said first and second chambers and having anopening providing communication between said first and second chambers,supportive means in said first chamber for supporting a material holderfor said semiconductor material, means for drawing a vacuum in saidfirst chamber, means associated with said first chamber for depositingan epitaxial coating on said semiconductor material, a removable coversealing said opening in the common Wall, a chamber forming wallassociated with said second chamber and having an opening therein, asecond removable cover sealing the opening in the chamber forming wall,a rack member disposed in said second chamber and adapted to support theholder of the semiconductor material, a glove member attached to andsealing a further opening in said chamber forming wall, said glovemember extending into said second chamber enabling manipulation of saidcovers by an operator in order to engage or disengage said materialholders for said semiconductor material with respect to said rack memberand said supportive means without causing communication between saidchambers and the atmosphere.

2. An apparatus for depositing an epitaxial coating on a semiconductormaterial removably disposed on a material holder, said apparatuscomprising an outer housing, means in said housing forming first andsecond chambers, a common wall extending between said first and secondchambers, means in said wall providing temporary communication betweensaid first and second chambers, first supportive means in said firstchamber for supporting a material holder for said semiconductormaterial, means for drawing a vacuum in said first chamber, meansassociated with said first chamber for depositing an epitaxial coatingon said semiconductor material, a chamber forming wall operativelyassociated with said second chamber, means in said chamber forming wallprovidingy temporary communication between said second chamber and theatmosphere external to said second chamber, second supportive meansdisposed in said second chamber and adapted to support a material holderfor the semiconductor material, manipulative means operativelyassociated with said housing for enabling operative communication withsaid second chamber so that an operator may engage or disengage saidmaterial holders from said supportive means without causingcommunication between said chambers and the atmosphere external to saidchambers.

3. An apparatus for depositing an epitaxial coating on a semiconductormaterial, said apparatus comprising' an outer housing, first partitionedmeans in said housing forming a first permanent chamber, secondpartitioned means in said housing forming a second permanent charnber,third partitioned means in said housing forming a third permanentchamber, iirst closure means operatively associated with said iirstpartitioned means providing operative communication between said firstand second chambers when open and a gas-tight seal therebetween whenclosed, second closure means operatively associated with said secondpartitioned means providing operative communication between said secondand third chambers when open and a gas-tight seal therebetween whenclosed, third closure means operatively associated with said thirdpartitioned means providing operative communication between said thirdchamber and the atmosphere external to said housing when open and agas-tight seal therebetween when closed, supportive means in said iirstcharnber for supporting a semiconductor material, and means associatedlwith said rst chamber for enabling deposition of an epitaxial coating onsaid semiconductor material.

4. The apparatus of claim 3 further characterized in that means isoperatively associated with said first chamber for purging theatmosphere of said iirst chamber.

5. The apparatus of claim 4 further characterized in that means isoperatively associated with said second chamber for purging theatmosphere of said second chamber.

6. The apparatus of claim 3 further characterized in that manipulativemeans is operatively associated with said housing for enabling actuationaf said first and second closure means to permit movement of saidsemiconductor material between the respective chambers.

References Cited UNITED STATES PATENTS 2,413,987 1/1947 Maxson.

2,580,976 1/1952 Toulmin 11S- 49.5 2,996,412 8/1961 Alexander 219-553 X3,051,164 8/1962 Trexler 128-1 X 3,086,882 4/1963 Smith et al. 118-491 X3,131,098 4/1964 Krsek et al. 148--175 3,197,328 7/1965 Jung et al.266-5 X 3,206,322 9/1965 Morgan 11S-49.1 X 3,272,199 9/ 1966 Matthews.

3,145,208 8/1964 Cheroff et al. 18-48 X FOREIGN PATENTS 1,291,661 3/1962France.

488,131` 7/1938 Great BritainY MORRIS KAPLAN, Primary Examiner U.S. Cl.X.R.

